Angular leaf spot of strawberry is caused by the bacterium Xanthomonas fragariae. The disease is disseminated primarily through systemically infected nursery stock. This creates problems for nurseries wishing to export plants to Europe because of quarantine restrictions. Currently, field inspections for symptoms are used to certifyplants free of X. fragariae, but visual inspection is not useful for detecting plants infected systemically. To detect systemic infections, PCR is the desired tool because of its sensitivity, specificity, and ease of use. In our research, we developed three sets of real-time PCR primers and probes – based on a set of standards PCR primers – and determined optimal reaction conditions for use of these primers (Poster Link #1). Real time detection proved to be both more sensitive and specific than standard PCR. Moreover, the detection of X. fragariae in crown tissue extract was possible with real time PCR but not with standard PCR which is a significant improvement over standard PCR. The information on sensitivity and specificity of the primer sets was used to evaluate the performance of these primers with receiver operating characteristic (ROC) curve analysis under different tolerances for the disease (Poster Link #2). The results of this analysis can be used to provide guidance on threshold selection to manage disease below unacceptable levels. We are also working on optimizing a hot water or heat treatment for killing X. fragariae in systemically infected plants (Poster Link #3), as this technique has been proven to be an effective procedure for killing systemic pathogens in other crops. We have worked with a number of heat treatment protocols in small-scale trials and are attempting to adapt this procedure for use in commercial nurseries.

19. Peres, N.A., Siejo, T.E., and Turechek, W.W. 2010. Pre- and Post-Inoculation Activity of a Protectant and a Systemic Fungicide for Control of Anthracnose Fruit Rot of Strawberry under Different Wetness Durations. Crop Protection 29:1105-1110.

20. Turechek, W.W., Kousik, C.S., and Adkins, S. 2010. Distribution of Four Viruses in Single and Mixed Infections within Infected Watermelon Plants in Florida. Phytopathology 100:1194-1203.